patch 8.0.0421: diff mode wrong when adding line at end of buffer

Problem:    Diff mode is displayed wrong when adding a line at the end of a
            buffer.
Solution:   Adjust marks in diff mode. (James McCoy, closes #1329)
diff --git a/src/version.c b/src/version.c
index f3a0b6c..c55ba19 100644
--- a/src/version.c
+++ b/src/version.c
@@ -765,6 +765,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    421,
+/**/
     420,
 /**/
     419,